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Temperature dependence of amino acid hydrophobicities

投稿者: Yuma Morimoto

  • Charles W. Carter, Jr.

    • Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599

    1. Contributed by Richard Wolfenden, April 20, 2015 (sent for review February 16, 2015; reviewed by Robert L. Baldwin, George D. Rose, and D. Peter Tieleman)

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    Abstract

    The hydrophobicities of the 20 common amino acids are reflected in their tendencies to appear in interior positions in globular proteins and in deeply buried positions of membrane proteins. To determine whether these relationships might also have been valid in the warm surroundings where life may have originated, we examined the effect of temperature on the hydrophobicities of the amino acids as measured by the equilibrium constants for transfer of their side-chains from neutral solution to cyclohexane (Kw>c). The hydrophobicities of most amino acids were found to increase with increasing temperature. Because that effect is more pronounced for the more polar amino acids, the numerical range of Kw>c values decreases with increasing temperature. There are also modest changes in the ordering of the more polar amino acids. However, those changes are such that they would have tended to minimize the otherwise disruptive effects of a changing thermal environment on the evolution of protein structure. Earlier, the genetic code was found to be organized in such a way that—with a single exception (threonine)—the side-chain dichotomy polar/nonpolar matches the nucleic acid base dichotomy purine/pyrimidine at the second position of each coding triplet at 25 °C. That dichotomy is preserved at 100 °C. The accessible surface areas of amino acid side-chains in folded proteins are moderately correlated with hydrophobicity, but when free energies of vapor-to-cyclohexane transfer (corresponding to size) are taken into consideration, a closer relationship becomes apparent.

    アミノ酸の疎水性の、温度依存性に関する研究です。高温領域で、常温と比べてどれくらい疎水性が変わるかについて議論しています。水とシクロヘキサンの二層系にアミノ酸を入れ、分配係数によって疎水性を評価しています。


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